Relationship between NRT measurements and behavioral levels in children with the Nucleus 24 cochlear implant may change over time: preliminary report

Objective: Response from spiral ganglion cells to electrical stimulation vi a the Nucleus 24 cochlear implant can be measured using the neural response telemetry system. The purpose of this study was to assess, in children, th e correlation between the neural response threshold and the behavioral leve ls used for cochlear implant programming process. Methods: The neural respo nse telemetry test was administered to 23 children (mean age at implantatio n: 4 years) with the Nucleus 24 cochlear implant. Four intra-cochlear elect rodes (electrodes 5, 10, 15 and 20) were tested. The neural response thresh old at 3, 6, 9 and 12 months post-implantation was compared with the behavi oral threshold and the maximum comfort level estimated during the same peri ods: a Pearson's correlation test was performed for each tested electrode. Results: On apical electrodes, the correlation with the behavioral threshol d remained significant from 3 to 12 months post-implantation (r ranging fro m 0.696 to 0.909, P < 0.05), and the correlation with the maximum comfort l evel was also significant throughout the study period, except on electrode 15 at 9 months (tendency to significance). On basal and intermediate electr odes, statistical correlations were found only at some points of time: none theless, at 12 months post-implantation, a significant correlation with beh avioral levels could be clearly demonstrated both on electrode 15 (r = 0.91 4-0.778, P < 0.05) and on electrode 10 (r = 0.845-0.720, P < 0.05). Conclus ions: This preliminary study suggests that the correlation between the neur al response threshold and behavioral levels may improve from the base towar ds the apex of the cochlea. However, a significant correlation can be demon strated for all tested electrodes at 12 months post-implantation. During th e first months post-implantation care must be exercised when interpreting n eural response telemetry measurements: a positive test does not necessarily mean that the stimulus delivered to the acoustic nerve will be centrally p rocessed with the result of an auditory perception. (C) 2001 Elsevier Scien ce Ireland Ltd. All rights reserved.